I'm a tad surprised as well!
I would say my 400 is probably the same or maybe slightly better condition than that one and I paid £700 for it the tail end of 2014.
That's some increase - I think as JohnR once said (or was it you Fossie?), "the world's gone mad!"
I'm assuming it's in part due to the new Katana publicity. There was not to bad GSF400 on ebay the other week (OK needed a little work on the carbs

) only went for £510 - a steal in comparison.